<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>输出内容</title>
</head>
<body>
    <script>
        // alert(msg)  弹出内容
        alert('hello')

        // document.write(msg) 在文档中输出内容
        document.write('hello')

        // console.log(msg) 在开发者工具的控制台console中输出内容
        console.log('hello')
    </script>
</body>
</html>